Did the Drilling and Deburring, Now Back to Dimpling....

After a long period of time, the length of which I can't even recall, I finally got to dimple some metal last night and tonight. It started last night by clearing off the work bench to make room for the dimpling table and C-Frame tool. Here is the table with the C-Frame in place and the subskin ready to go. After I countersunk the rivet holes for the nut plates that surround the access panel hole, my next task was to dimple the Screw holes with a # 8 dimple die, which is visible through the first of several holes in the subskin in the next pic after this one:

In this next pic which is a close up, see if you can find the problem that almost cost me months and months of work:

Do you see it? Before I divulge the answer, I just have to say that it was such a joy to setup my dimpling table on the "new and improved" work bench, where all the table legs fit on a truly flat workbench, without the need for a hinged extension like the one I had to use so many times before while building the tail section. I was waiting for the day when the decision to go with the solid core door as mt new bench would pay off. It is still a pain in the ass to have to adjust all the adjustable table legs to get the table correctly leveled with the dimple dies, since I do not have "easy" access to the rear of the table, which is up against the wall/pegboard. This makes it a bit difficult to adjust the rear leg height, but I managed to get it done. Another challenge is that with the wing currently on the stand, and the bench being a few inches wider than before, I have less effective space to work with when lifting the table onto the work bench. it wasn't too bad to get it up there, but I still had to be careful not to hit the wing.



Now, back to the pic, do you see it yet? Or rather, I should be asking, do you NOT see it yet? The male dimple die is mounted on the bottom of the C-Frame, and the guide pin from that die is visibly sticking up through the hole. BUT..... To make a dimple, you need to have both a male AND a female die. If you guessed that the female die is not mounted on the ram just above the hole, then you were correct.


In my haste to get to dimpling I had set up everything else correctly, but I forgot the final step of inserting the female die into the ram. And then, yes, for that first hole, I held down the ram over the pin of the male die, and whacked it a few times. After removing the ram I inspected the "dimple" and found it to be very shallow and it did not look right. It also had a very strange looking rim at the bottom of the so-called dimple. It was then that I realized what I had done. (Or not done in this case).



The good news is that, after I inserted the female die into the ram and struck it again, this time the dimple looked like a dimple, although it still has the funny looking edge at the bottom. I test fitted it with the nut plate, and everything fit just fine. So then I finished dimpling all the remaining #8 screw holes.



With the screw holes in the subskin done, the next step was to dimple the access panel cover plate.

And here is the result of the cover plate dimples. Turned out pretty good I think:

And I got the same results for the matching subskin dimples:

I trimmed away a little too much metal in one corner of the opening, so I took a couple of files and radiused that corner just a bit more, and then I trimmed away a little more excess metal on the straight edges. SO what do you do when you finish dimpling two parts that are supposed to fit together - trial fit them of course! This next pic has a #8 screw in one of the holes to see how it will look with the plate secured to the subskin:

Next came the final prep of the rivet holes for each K1100-8 nut plate. After countersinking the holes for the NAS 1097 rivet heads, this exposed some unprimed metal. So I needed to perform the same trick I came up with  a long time ago when I countersunk all those fuel tank nut plate holes. I used a tapered Que-Tip  (NOT the standard round-headed ones, but specifically tapered and cone-shaped), and some NAPA 7220 self etching primer in a cup, to lightly coat each of the countersunk holes with some primer.



IN this next pic, pay close attention to the white plastic cup in front of the box of Q-Tips:

I shook up the spray can of primer really well, and sprayed some excess primer into the bottom of the cup. I sprayed just enough to allow the Que tip to get enough primer to cover each rivet hole as shown below (pic is a bit blurry - sorry bout that!).

Just insert the primer soaked Q-tip into the rivet hole, remove, and move to the next hole and do it again. After doing a few holes, you figure out how much pressure to apply to deliver the right amount of primer on the edges of each countersunk hole. Excess primer is not much of a problem - you just scrape it away from the edges as necessary. it is also important to test fit the rivets in the hole after you do this. If you get too much primer in there then you can take a deburring bit and run it just enough to either reduce or eliminate the primer, and re-fit the rivet and reapply primer as necessary.



Now for the rest of the story. I almost had another "accident" here that could easily have caused several nasty problems. Luckily, I managed to "escape" relatively unharmed. This next pic shows the bag of the plastic "bath" cups that I used. I guess these are supposed to resemble the old paper Dixie cups, and are designed for holding small amounts of water for rinsing after you brush your teeth, etc.

I primed a few holes, and then paused briefly to check the holes with the applied primer, and I set the cup down on the bench for only a minute or two. Also note that I am doing all this right on top of my carpeted dimpling table. (Not a good idea). When I went to pick up the cup again to saturate the Q-tip one more time, the entire bottom of the cup completely separated from the rest of the cup, and started spilling any remaining liquid primer that was still in the cup.


Most of it ended up dripping on the subskin and my hands and fingers, and luckily there was not very much liquid remaining in the cup. I also thought that some of it splashed onto my work clothes, which I was still wearing for this event, but I seemed to have escaped that disaster as well. But I still had several more holes to prime, so what was I going to use for a container, knowing that using this particular cup was now out of the question?



I had also purchased some different condiment cups a long time ago, as shown in the next pic, that I had also never used before.

Now that I was much more alert as to the potential problems that a plastic container and highly volatile primer might cause when combined together, I knew that I would test this situation out for several minutes by keeping the container on the work bench the entire time, sitting on top of several paper towels - just in case. This time, though, after several minutes, nothing bad happened, and the container seemed to "hold its own" with the primer:

So, several lessons learned (or re-learned) here -
DON'T use the first cups for any type of chemical mixing without testing it first.
DON'T wear your good clothes when priming stuff.
DON'T pick up the cup and hold it near critical tools or parts unless you are certain that retains its viability as a container. (And is not melting away in your hand or smoldering, etc.)


I think that each different cup is made with a different type of plastic, and one is obviously more resistant to the chemicals in the primer than the other.




The next task was to dimple the permanent cover plate with my 3/32 inch dimple dies. So I had to change out the dies in the C-Frame for the smaller holes in the patch plate.

I could have used the pneumatic squeezer for all of the cover plate holes, but I wanted to continue to practice with the C-Frame, since I am going to be using it for quite a while in the near future to dimple the LE, Fuel tank, and main wing skins and ribs. Lots and lots of holes to dimple and countersink. So the more practice I get with the C-Frame the better.



And now the results:

Then it was back to the subskin to dimple all matching holes in that part:

I had been trying to decide if I was going to dimple one final hole that ended up being very close to another hole for the permanent patch plate. This was just the result of a measuring issue where I had already drilled a hole that matched an existing hole in one of the mounting plates that I decided to use as a template for the subskin. Afterward, I decided that I also needed rivet holes about 1/4 inch away from each of the edges. So this resulted in two of those holes being very close together. Anyway, I finally decided to go ahead and dimple it, after seeing that the dimples were far enough apart so that they would not interfere with each other. I did this in the holes for in the patch plate and the subskin.
I will also need to dimple this hole in the outer LE skin. Hopefully it all comes out OK. I think it will.



Tonight I finished (almost) dimpling the remaining 3/32 holes for the subskin for the perimeter holes for what would have been the mounting plate for each access panel, and all but 8 of the most forward LE holes in the subskin, which will need to be dimpled with the close quarter dimpling tool, since the bend in the skin is too stiff to dimple them safely with the C-Frame. I will also need to use the same tool for dimpling the rib flanges that correspond to these same holes.



I also need to scuff, clean, and prime each cover plate. This last pic shows the fit of each plate against the subskin after the dimples were formed. Everything fit together amazingly well. I won't set the rivets on the permanent patch plate to the subskin until I have reassembled the entire LE again, to make sure that the fit between the patch plate and the outer skin is also good.

Everything aligned really, really well after setting all these dimples, and there was not much distortion or bending of the parts either, so I am happy about that.


Another "next" step is to rivet my nut plates for the access panel to the subskin (Yes, another thing I have not done in forever). I spent some time today trying to figure out how to secure the subskin to the bench for this. Anytime I have to do this for some sort of pre-bent skin, you have to get very creative about how you secure and stabilize the part. I'll elaborate more on my thought process for that tomorrow.


One thing you can count on, is that it will involve a lot of clamps and a lot of uniquely shaped and positioned clamping blocks to ensure that I have the security, rigidity, and stability that I need to properly rivet them in place. I also want to make sure that I position the part so that I can apply pressure on the pneumatic squeezer on the non-moving part of the yoke against the manufactured head of the rivet, so that the moving part of the squeezer will be against the rivet stem. Then, once I get all that figured out, I try to position everything so that the squeezer is in my right (dominant) hand, and my left hand is free for holding the part, etc. That bit of wisdom comes from a lot of learning about riveting from actual experience, which you just can't find in any of the text books or the classes. Thankfully I still remember how to apply those experiences.



More tomorrow

KPR